#include <bits/stdc++.h>
using namespace std;
bool check(char arr1,char arr2)
{
  if((arr1=='A'&&arr2=='T')||(arr1=='T'&&arr2=='A'))
    return true;
  if((arr1=='C'&&arr2=='G')||(arr1=='G'&&arr2=='C'))
    return true;
  return false;
}

int main()
{
  ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
  int n=0; cin>>n;
  string arr1;cin>>arr1;
  string arr2;cin>>arr2;
  int count=0;
  for(int i=0;i<n;++i)
  {
    if(check(arr1[i],arr2[i])) continue;
    for(int j=i+1;j<n;++j)
    {
      if(check(arr1[i],arr2[j])&&check(arr1[j],arr2[i]))
        {
          swap(arr2[i],arr2[j]);
          break;
        }
    }
    count++;
    }
  cout<<count;

  return 0;
}
